Luminescent material



Sept. 27, 1955 G. KREssm LUMINESCENT MATERIAL Filed May 11, 1954 OE1 0.1om

ON Of OOK` um4 om Oh om Om@ OJ om ou Oe OO@ om om on om 0mm o# om ou OfOom O Of mp ON mm Om mn C: me

mm om mo oh 2. om mm om m OO lnvenor @En Re. KREss//y' United StatesPatent c(")iiice 2,719,128 Patented Sept. 27, 1955 LUMINESCENT MATERIALGeorg Kressin, vBerlin-Frohnau, Germany, assignor toPatent-Treuhand-Gesellschaft fr Elektrische Glhlampen rn. 'b. H.,Heidenheim (Brenz), 'Germany Application May 11, 1954,.Serial No.429,088 Claims priority, application Germany, June 21,1950 1'1 Claims.A(Cl. 252-301.@

The luminescent materials of the present invention may I also be appliedon the outer Wall of the bulb or on a screen inf front of the dischargelamp. In this case, the

Ienvelope of thedischarge lamp must be capable of transmitting theexciting-radiation.

Thel presenty case is a continuation-in-part of my copendingapplication, Serial No. 232,655, iiled June 20, 1951 for LuminescentMaterial, now'abandoned.

Phosphorswhich in general consist of a major proportion of a basematerial or matrix and a minor proportion` of another material called anactivator and consisting of one or more substances which act as theAactivator vhave been produced whereinthe matrixzconsists of calciumsilicate and the activator consists of lead and manganese.

Although-the red'emission of suchsphosphor isrelatively high as`compared to other known phosphors, the red emission is still notsufliciently intense in the longer red wavelengths for many purposes andthe percentage of shorter wave length emission in the yellow-green isalso relatively high. Increased. red` emission is obtained in suchcalcium-silicate phosphors by increasing the manganese percentage of thelead and manganese activators.

However, such. luminescent materials having a high percentage ofmanganese show a reduced stability of lighting intensity and have thefurther disadvantage that they arei diilicult to prepare due to the highpercentage of manganese. Moreover, such phosphors tend to have acharacteristic brown coloring caused by the increased amount of heavymetal therein.

It is therefore a primary object of the present invention to provide anovel luminescent material or phosphor which exhibitsl a marked increasein red emission with a corresponding decrease in yellow-green emission.

It is another object of the present invention to provide novelluminescent material which has an increased red emission'as compared tocalcium-silicate phosphors without increasing the content of manganesein the phosphor.

It is yet another object of the present invention to provide coated lowpressure mercury discharge lamps coated with the luminescent material ofthe present invention and. thereby having improved red emission.

It is a` further object of the present invention to provide a process ofproducing the novel phosphors of the present invention.

It is still a further object of the present invention to providecolorless or substantially colorless phosphors having a strong redemission.

As a further object, the present invention comprises the production ofmixed crystals of strontium silicate and calcium silicate activated bylead and manganese which `weight of the entire phosphor..

Vupon excitation by ultra-violet rays, X-rays or cathode rays luminescewith a high red emission.

Other objects and advantages of the present invention -Will be.apparent' from the further reading of the specification and of theappended claims.

With thev above objects in View, thepresent invention mainly comprises anovel luminescent materialadaptedto be excited by'ultra-vio'letrays,X-rays andcathode 'rays to emit light, the luminescent material`essentially consisting of 'lead and manganese activatedcalcium-strontium-silicate containing `between 0.0l-0g06 molestrontium-per each mole of calcium and strontium and 'between 1 0-'1.25moles of silica per each mole of calcium and strontium.

According to va preferred embodiment of the present invention the innerwall of low pressure mercury discharge lamps are coatedwith theluminescent .material of the. present invention. This coating may becarried out inA 'the normal mannerfor. coating tube or bulb walls withphosphors.

The amount of lead and manganese as activators in the phosphor may varywithin relatively wide limits Within which'the concentration ofactivators in known phosphors may vary. However, it is a primaryadvantage of .the present invention thatthe` amount of heavy metalactivator inthephosphors of the present invention may be kept low whileachieving a strong red emission. It is therefore preferred to maintainthe amount of lead and'manga'nese to within 1-3% by weight of each ascompared to the Most preferably, the amount of lead in the form oflead'oxide in the phosphor is about 1.6% by weight and the amount ofVmanganese in the form of'manganese carbonate is 2.4% by weight oftheventire phosphor.

The method of manufacturing the luminescent materials ofl the presentinvention mainly comprises the steps of mixingcalcium-andstrontiumcompounds, namely the oxides or compounds which form the oxides uponheating, i; e.,vthe carbonates, with silica and with lead and manganesecompounds. The ratio of strontium compound in the mixture is between0.01-0.06 mole of the strontium compound' per mole of the strontiumcompound'plus the calcium compound. In other Words there i's'between0;01`-0.06 mole lof strontium to about 099-094 mole of calcium. Theamount of silicate in the' mixture is between 1fl.25 moles of silica pereach mole of calcium and strontium. Preferably the mixture consists of0.95` mole of calcium:0;05 mole of strontiumrl moles of silica. Anotherpreferred composition consists of 0.973 moleof calcium:0.027 mole ofstrontium: 1.1 moles of silica. Actually in the finalcalcium-strontiurn-silicate composition the calcium is in the form ofCaO, the strontiumis in the form of SrO and the silica of course asSiOs.

The lead compound with which the calcium compound, the strontiumcompound and the silica are mixed is preferably lead oxide. Themanganese compound is preferably manganese oxide or manganese carbonate,and most preferably manganese carbonate.

The formed mixture is then heated to calcining at a temperature suchthat reaction takes place between the calcium compound, e. g., calciumcarbonate, the strontium compound, e. g., strontium carbonate, and thesilica to form the calciumstrontium-silicate phosphor containingthe leadand manganese activators. The heating is preferably carried out in anatmosphere of steam so as to prevent oxidation during heating.Preferably the heating is carried4 out at a temperature between1100-1200.o C.

It is preferred to alternately heat the mixture, e. g., at about ll00C., then mill and sift the heated material, and then heat again threeadditional times at a temperature of about 1100-l200 C. for 1,1/2 hourseach time,

a each heating period being followed by a milling and sifting step.

It has been found that by increasing the percentage of strontium at thesame concentration of activators the red portion of the emittedradiation will increase whereas the yellow-green portion decreases; atthe same time the emission maximum will be shifted towards the longwaves. According to the present invention luminescent materials areobtained by means of the calcium-strontium-silicates which have aconsiderably higher red proportion of the emission than do calciumsilicates having the same concentration of activators.

In order to better illustrate the advantageous results obtained by thenovel luminescent phosphors of the present invention, there is herewithattached a drawing consisting of a graph comparing the radiationintensity in arbitrary units of a lead and manganese activated calciumsilicate phosphor with lead and manganese activatedcalcium-strontium-silicate phosphors of different strontiumconcentration, the concentration of lead and manganese activators alwaysremaining constant.

The emission curves in the annexed diagram show the radiation intensityin arbitrary units depending on the wave-lengths in mit =Angstrom). Thecurves are delineated for luminescent materials with equalactivator-concentration with a percentage of manganese oxides of 1.15%by weight and a percentage of lead oxide of 1.75% by weight. Curve 1shows the emission of a calcium-silicate (Mn-l-Pb) without any strontiumfor the purpose of comparing, curve 2 the emission of a Ca-Sr-silicate(Mn-l-Pb) with a percentage of Sr of l mole percent, curve 3 shows theemission of a Ca-Srsilicate (Mn-i-Pb) with a percentage of Sr of 2.5mole percent and curve 4 the emission of a Ca-Sr-silicate (Mn-l-Pb) witha percentage of Sr of 5 mole percent.

It may be clearly seen that with a constant activatorconcentration, theemission decreases in the yellow-green part and increases in the redpart with simultaneous shifting of the emission maximum towards thelonger wavelengths. It is clear from the diagram that by the manufactureof Ca-Sr-silicates activated with (Mn-l-Pb) according to the presentinvention luminescent materials are obtained the emission of which ismainly in the red part of the spectrum.

An increase of the red emission by incorporating strontium silicate witha constant activator-concentration is, `of course, only possible withinthe range of formation of mixed crystals between calcium silicate andstrontium silicate. The maximum limit for the formation of mixedcrystals is about 6 mole percent. A further addition of strontiumsilicate to the luminescent material has no inuence on it but causes adecreasing of the light intensity. Although any amount of strontiumsilicate in the phosphor increases the percentage of red emissionthereof, a marked increase occurs within an amount of l mole percent ofstrontium-silicate and this is therefore the minimum amount ofstrontium-silicate in the composition of the present invention.

The following examples are additionally illustrative of the presentinvention and are not to be considered as limiting the scope thereof.

Example I 0.973 mole of calcium carbonate and 0.027 mole of strontiumcarbonate, previously dried at a temperature of about 150 C., areintimately mixed with 1.1 moles SiOz to which are added 1.6% by weightof lead oxide and 2.4% by weight of manganese carbonate. This intimatemixture is heated in a stream of steam at a temperature of about1100-1200 C. several times, each heating period being followed by amilling and sifting operation. A very tine luminescent powder of Pb-Mnactivated Ca-Sr-silicate exhibiting a high luminous ux of yellowishradiation is produced.

-l Example Il 0.95 mole of calcium carbonate and 0.05 mole of strontiumcarbonate, previously dried at a temperature of about C., are intimatelymixed with 1.1 moles SiOz to which are added 1.6% by weight of leadoxide and 2.4% by weight of manganese carbonate. This intimate mixtureis heated in a stream of steam at a temperature of about 1l0O-l200 C.several times, each heating period being followed by a milling andsifting operation. A very line luminescent powder of Pb-Mn activatedCa-Sr-silicate exhibiting a high luminous ux of red radiation isproduced.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A novel luminescent material adapted to be excited by ultravioletrays, X-rays and cathode rays to emit light, said luminescent materialessentially consisting of lead and manganese activatedcalcium-strontium-silicate containing between 0.01-0.06 mole strontiumper each mole of calcium and strontium and between 1.0-1.25 moles ofsilica per each mole of calcium and strontium; and containing betweenl-3% each of lead and manganese.

2. A novel luminescent material adapted to be excited by ultravioletrays, X-rays and cathode rays to emit light, said luminescent materialessentially consisting of lead and manganese activatedcalcium-strontium-silicate containing 0.05 mole strontium per each moleof calcium and strontium and 1.1 moles of silica per each mole ofcalcium and strontium; and containing between l-3% each of lead andmanganese.

3. A novel luminescent material adapted to be excited by ultravioletrays, X-rays and cathode rays to emit light, said luminescent materialessentially consisting of lead and manganese activatedcalcium-strontium-silicate containing 0.027 mole strontium per each moleof calcium and strontium and 1.1 moles of silica per each mole ofcalcium and strontium; and containing between 1-3% each of lead andmanganese.

4. A novel luminescent material adapted to be excited by ultravioletrays, X-rays and cathode rays to emit light, said luminescent materialessentially consisting of lead and manganese activatedcalcium-strontium-silicate containing 0.05 mole strontium per each moleof calcium and strontium and 1.1 moles of silica per each mole ofcalcium and strontium; and containing about 1.6% lead oxide and 2.4%manganese carbonate.

5. A novel luminescent material adapted to be excited by ultravioletrays, X-rays and cathode rays to emit light, said luminescent materialessentially consisting of lead and manganese activatedcalcium-strontium-silicate containing 0.027 mole strontium per each moleof calcium and strontium and 1.1 moles of silica per each mole ofcalcium and strontium; and containing about 1.6% lead oxide and 2.4%manganese carbonate.

6. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of forming amixture of lead oxide, a manganese compound selected from the groupconsisting of manganese oxide and manganese carbonate, silica andcalcium and strontium compounds selected from the group consisting ofoxides and compounds producing oxides upon heating, in a ratio ofbetween G01-0.06 mole strontium compound per each mole of calcium andstrontium compounds, 1.0-1.25 moles silica per each mole of calcium andstrontium compounds and 1-3% lead oxide and 1-3% of said manganesecompound by weight of said mixture; calcining said mixture at atemperature sufficiently high to cause reaction among said calcium andstrontium compounds and said silica, thereby forming acalcium-strontium-silicate phosphor activated by lead and manganese; andrecovering said thus formed phosphor.

7. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of forming amixture of lead oxide, a manganese compound selected from the groupconsisting of manganese oxide and manganese carbonate, silica andcalcium and strontium compounds selected from the group consisting ofoxides and compounds producing oxides upon heating, in a ratio ofbetween Q01-0.06 mole strontium compound per each mole of calcium andstrontium compounds, 1.0-1.25 moles silica per each mole of calcium andstrontium compounds and 1-3% lead oxide and 1-3% of said manganesecompound by weight of said mixture; calcining said mixture at atemperature of about 1100-1200 C. so as to cause reaction among saidcalcium and strontium compounds and said silica, thereby forming acalcium-strontium-silicate phosphor activated by lead and manganese; andrecovering said thus formed phosphor.

8. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of forming amixture of lead oxide, a manganese compound selected from the groupconsisting of manganese oxide and manganese carbonate, silica andcalcium and strontium compounds selected from the group consisting ofoxides and compounds producing oxides upon heating, in a ratio ofbetween 0.01-0.06 mole strontium compound per each mole of calcium andstrontium compounds, 1.0-1.25 moles silica per each mole of calcium andstrontium compounds and 1-3% lead oxide and 1-3% of said manganesecompound by weight of said mixture; calcining said mixture in anatmosphere of steam at a temperature of about 1100-1200 C. so as tocause reaction among said calcium and strontium compounds and saidsilica, thereby forming a calciumstrontium-silicate phosphor activatedby lead and manganese; and recovering said thus formed phosphor.

9. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of intimatelymixing calcium carbonate, strontium carbonate and silica in a ratio of0.01-0.06 mole strontium carbonate per each mole of strontium carbonateand calcium carbonate and 1.0-1.25 moles silica per each mole ofstrontium carbonate and calcium carbonate; adding to the said mixturebetween l-3% lead oxide and 1-3% manganese carbonate by weight of thethus formed mixture; heating said thus formed mixture in an atmosphereof steam at a temperature between about 1100-1200" C., thereby forming acalciumstrontium-silicate phosphor activated by lead and manganese; andrecovering the thus formed phosphor.

10. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of intimatelymixing calcium carbonate, strontium carbonate and silica in a ratio of0.05 mole strontium carbonate per each mole of strontium carbonate andcalcium carbonate and 1.1 moles silica per each mole of strontiumcarbonate and calcium carbonate; adding to the said mixture 1.6% leadoxide and 2.4% manganese carbonate by weight of the thus formed mixture;heating said thus formed mixture in an atmosphere of steam at atemperature between about 1100-1200" C., thereby forming acalcium-strontium-silicate phosphor activated by lead and manganese; andrecovering the thus formed phosphor.

11. A process of producing a lead and manganese activatedcalcium-strontium-silicate phosphor, comprising the steps of intimatelymixing calcium carbonate, strontium carbonate and silica in a ratio of0.027 mole strontium carbonate per each mole of strontium carbonate andcalcium carbonate and 1.1 mole silica per each mole of strontiumcarbonate and calcium carbonate; adding to the said mixture 1.6% leadoxide and 2.4% manganese carbonate by weight of the thus formed mixture;heating said thus formed mixture in an atmosphere of steam at atemperature between about 1100-1200 C., thereby forming acalcium-strontium-silicate phosphor activated by lead and manganese; andrecovering the thus formed phosphor.

References Cited in the le of this patent UNITED STATES PATENTS2,445,692 Porter et a1. July 20, 1948 2,447,210 Roberts Aug. 17, 19482,450,548 Gisolf et al. Oct. 5, 1948 FOREIGN PATENTS 577,694 GreatBritain May 28, 1946

1. A NOVEL LUMINESCENT MATERIAL ADAPTED TO BE EXCITED BY ULTRAVIOLETRAYS, X-RAYS AND CATHODE RAYS TO EMIT LIGHT, SAID LUMINESCENT MATERIALESSENTIALLY CONSISTING OF LEAD AND MANGANESE ACTIVATEDCALCIUM-STRONTIUM-SILICATE CONTAINING BETWEEN 0.01-0.06 MOL STRONTIUMPER EACH MOLE OF CALCIUM AND STRONTIUM AND BETWEEN 1.0-1.25 MOLES OFSILICA PER EACH MOLE OF CALCIUM AND STRONTIUM; AND CONTAINING BETWEEN1-3% EACH OF LEAD AND MANGANESE.